Anal fistula is a common anorectal disease, accounting for 1.6-3.6% of anorectal diseases, and usually formed by rupture or incision of anorectal abscess. Compared with other diseases, anal fistula is characterized in extreme pain in patients, low surgical success rate, and probable recurrence, bringing about tremendous physical and psychological problems to the patients. Anal fistula treatment mainly comprises surgical incision, hanging line therapy, anal fistula excision, cryotherapy, and electrotherapy, etc. These treatments suffer from the defects of extreme pain during treatment, low cure rate (lower than 40%), long recovery period, and frequent recurrence. In recent years, based on findings in tissue engineering study, the use of biocompatible scaffolds for anal fistula repair bring a new dawn to the treatment of anal fistula. Compared with the traditional treatment methods, scaffold repair surgery has the advantages of reduced pains, improved success rate, fewer complications, lower recurrence rate, and has been generally accepted by patients in developed countries. In the current clinical trials, the prosthetic materials mainly used include fibrin gels and porcine small intestinal submucosa scaffold developed by Cook Medical, Inc. Among them, fibrin gels degrade rapidly, and yield an anal fistula cure rate of below 40%. Compared with fibrin gels, porcine small intestinal submucosa scaffold has improved degradation rate, and yields an increased anal fistula cure rate to about 50%. Nevertheless, its degradation rate still cannot fully meet the requirements of the treatment of anal fistula, and resulted in an anal fistula recurrence rate of 10% or greater. Moreover, it suffers from complex extraction and preparation process, high cost, and high price of around $2,000 each, which is unbearable to patients in China Thus, the treatment of anal fistula is urgent for the latest results in the tissue engineering studies, so as to develop new porous scaffolds having good biocompatibility, high mechanical strength, low degradation rate, and low price.
Silk fibroin is the main component of silk, which is inexpensive and easy to purify. Studies have shown that silk fibroin is non-toxic, non-immunogenic, well biocompatible, biodegradable, and excellent in mechanical properties. It is an ideal raw material for the preparation of tissue repair and tissue engineering scaffolds. Silk fibroin has different crystal structure including Silk I and Silk II. The difference in types and contents of crystals can determine the solubility and degradation of silk fibroin. By adjusting its crystal and non-crystal structure, the in vivo degradation rate of silk fibroin can be reduced from one year to about half a month, so as to meet the different needs of tissue repair and regeneration.
Currently, researchers have developed various methods for preparation of silk fibroin scaffolds, comprising a freeze-drying method, a phase separation method, a salting-out method and an electrostatic spinning method, etc. However, the above methods each have deficiencies difficult to overcome. For example, a silk fibroin scaffold prepared by salting-out typically has a pore size of 400 microns or more, and a porous material prepared by electrostatic spinning typically has a pore size of 100 microns or less. As such, there are restrictions for their use as a tissue repair or tissue engineering scaffold. A porous scaffold having a larger range of pore size can be prepared by freeze-drying. However, during the freezing process, the silk fibroin is liable to be self-assembled into a sheet structure, and it is difficult to obtain a good porous structure. In the prior art, a porous scaffold having a good pore structure and suitable for tissue growth has been successfully prepared by controlling the self-assembly of silk fibroin. However, the scaffold thus obtained faces a major problem in practical applications. It has relatively poor mechanical strength and weak tearing resistance, and therefore is difficult to be sutured and fixed by a surgical thread or to be operated by minimally invasive surgical operation, which results in that the scaffold cannot be practically used in clinical application, especially in anal fistula repair plugs.
Therefore, there is a need to overcome the above problems in the prior art, to develop a high-strength biological scaffold material having high tear resistance strength and suitable to be sutured and fixed by a surgical thread, and thereby to prepare a fibroin anal fistula repair plug in order to meet the practical needs.